A Senate panel approved a constitutional amendment yesterday that supporters say would ensure Congress could function in the aftermath of a devastating terrorist attack or other disaster.

The amendment would give Congress new powers to ensure the prompt replacement of lawmakers who are killed or incapacitated in such a strike. The Senate Judiciary subcommittee on the Constitution, headed by Sen. John Cornyn (R-Tex.), who sponsored legislation, passed it on a voice vote.

But one absent member, Sen. Edward M. Kennedy (D-Mass.), sent colleagues a letter saying it was "unwise to go forward" without consulting the House, and without first considering remedies that do not require changing the Constitution.

Constitutional amendments require two-thirds majority approval in the House and Senate and the ratification by three-fourths of the state legislatures.

Cornyn's measure would open the door for temporary appointees to fill in for gravely injured senators. The Constitution permits governors to appoint temporary replacements for senators only in the event of death.

More controversially, the proposed constitutional amendment would allow Congress to pass a law permitting the appointment of temporary replacements for killed or injured House members. That idea is deeply unpopular with House GOP leaders, who believe the constitutional requirement that all House members be elected makes the chamber uniquely reflective of the people's will.

Cornyn acknowledged the opposition in the House but said the continuing threat of a terrorist attack meant that the Senate should press the issue.

"We ought not make the perfect be the enemy of the good," said Cornyn, who added that he was optimistic his proposal would win full committee approval and reach the Senate floor this year. "It's important that we do something and move forward."

On April 22, the House passed a measure that would require states to hold special elections within 45 days if at least 100 members are killed in an attack. Separately, the House Rules Committee is exploring whether changes in House rules could help mitigate the possibility of incapacitated members.

The House Judiciary Committee also last week sent to the full House a proposed constitutional amendment by Rep. Brian Baird (D-Wash.) that would allow governors to appoint temporary replacements to the House. But the panel recommended that lawmakers defeat it.

Jeff Lungren, a spokesman for the House Judiciary Committee, said Cornyn's amendment was unlikely to make it that far. Lungren noted that three times during the Cold War the Senate approved amendments allowing for the appointment of House members. The House, led one of those times by Republicans and the other two times by Democrats, rejected all of the measures, he said.

Sen. Russell Feingold (D-Wis.) said at the subcommittee meeting yesterday he agreed that requiring all House members be elected makes that chamber "very special." Although he rarely believes constitutional amendments are necessary, the threat of a Congress that cannot function warrants such a step, he said.

"The Constitution of this country was not a rough draft. We should not treat it as such," Feingold said. ". . . . This is a rare situation where a constitutional amendment is justified."